Spatial variation in vegetation damage relative to primary productivity, small rodent abundance and predation

Abstract

The relative importance of top‐down and bottom‐up mechanisms in shaping community structure is still a highly controversial topic in ecology. Predatory top‐down control of herbivores is thought to relax herbivore impact on the vegetation through trophic cascades. However, trophic cascades may be weak in terrestrial systems as the complexity of food webs makes responses harder to predict. Alternatively, top‐down control prevails, but the top‐level (predator or herbivore) changes according to productivity levels. Here we show how spatial variation in the occurrence of herbivores (lemmings and voles) and their predators (mustelids and foxes) relates with grazing damage in landscapes with different net primary productivity, generating two and three trophic level communities, during the 2007 rodent peak in northern Norway. Lemmings were most abundant on the unproductive high‐altitude tundra, where few predators were present and the impact of herbivores on vegetation was strong. Voles were most common on a productive, south facing slope, where numerous predators were present, and the impacts of herbivores on vegetation were weak. The impact of herbivores on the vegetation was strong only when predators were not present, and this cannot be explained by between‐habitat differences in the abundance of plant functional groups. We thus conclude that predators influence the plant community via a trophic cascade in a spatial pattern that support the exploitation ecosystems hypothesis. The responses to grazing also differed between plant functional groups, with implications for short and long‐term consequences for plant communities.

Effects of elevation and nitrogen and phosphorus fertilization on plant defence compounds in subarctic tundra heath vegetation

“…; Hoset et al . ). Further, shifts in the type of phenols that the plant community produces with changing elevation may explain several of the observed interactions between N addition and elevation that we observed.…”

“…; Hoset et al . ), which may also lead to increases in plant defence at both the highest and lowest elevations. In the present study, we utilized a subarctic elevational gradient near Abisko in northern Sweden (Sundqvist, Giesler & Wardle ; Sundqvist et al .…”

Predator–rodent–plant interactions along a coast–inland gradient in Fennoscandian tundra

“…The intensity of rodent herbivory on tundra vegetation is also expected to vary in space due to landscape heterogeneity in the composition of plant, rodent and predator communities. For example, weak rodent impacts on arctic vegetation have been documented in areas where predation forces were strongest, probably caused by three‐level trophic cascades (Aunapuu et al ), even in years of high rodent abundance (Bilodeau et al , Hoset et al ).…”

Loss of biotic resistance and high propagule pressure promote invasive grass‐fire cycles

“…Second, other disturbances including grazing which is widespread in the Great Basin disrupt native vegetation and soil crusts (Beck & Mitchell, ; Kaltenecker et al, ) that promote cheatgrass establishment (Chambers et al, ). Finally, rodent populations naturally fluctuate, including periods in which their populations crash resulting in establishment opportunities for invasive grasses without top‐down pressure from rodent consumers (Hoset, Kyro, Oksanen, Oksanen, & Olofsson, , Sharp‐Bowman et al, ). Once cheatgrass establishes due to these perturbations and fire is introduced into the system, post‐fire conditions create an ideal environment for the establishment and spread of cheatgrass that are linked to larger and more frequent fires (Balch et al, , Brooks et al, ).…”